Injectable male animal sterilant for selectively controlling the function of testes

ABSTRACT

An injectable chemical compound capable of producing sterility in male animals having scrotal testes for use in selectively controlling the exocrine function of the testes in the production of sperm and the endocrine function in the production of testosterone. Said injectable chemical compound being a physiologically acceptable astringent, preferably a water soluble zinc compound, a tannin or combinations thereof. Various concentrations of said compound being selectively injected directly into the testes or into the scrotum to suppress spermatogenesis and, optionally, to suppress production of testosterone.

This is a continuation-in-part of application Ser. No. 651,712, filed Jan. 23, 1976, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of drug, bio-affecting and body treating compositions, and more specifically to physiologically acceptable astringents for use in selectively controlling the exocrine function of the testes in the production of sperm and the endocrine function in the production of testosterone.

2. Description of the Prior Art

A large number and variety of chemical approaches have been tried to affect spermatogenesis in male animals. These approaches have included luteinizing hormones, testosterones, steroids and other steroidal derivatives. Examples of such compounds are described in U.S. Pat. No. 3,836,640.

In nearly all of these prior approaches, the compounds have been administered orally or injected into the body. None have proved chemically or commercially successful. Nearly all have failed because of adverse side effects or reduction of libido.

The spermicidal effects of many non-essential metals are also known and have been comprehensively reported. Gunn, Samuel A. and Thelma Clarke Gould, 1970, The Testis, Vol. III, Influencing Factors, 377-481. Many of the metals studied are normally considered as toxic in any form.

The presence of zinc in the male reproduction process is well established, but its mode of action is not clearly defined. Human seminal plasma normally contains a high concentration of zinc. Gallob-Hausmann, Gerda, Zinc and Its Physiological Relationship to the Human Body--A Review. However, there are indications that zinc ions under certain conditions can exert toxic effects on human spermatozoa. White, I. G., 1955, The Toxicity of Heavy Metals to Mammalian Spermatozoa, Austral. J. Exp. Biol. 33, 359-366. Rosado, A., et al. 1970, Inhibition of Human Sperm Motility by Calcium and Zinc Ions, Contraception 2, 259-273. Kesseru, E., et al. 1972, Influence of Metals in In Vitro Sperm Migration in the Human Cervical Mucus, Contraception 6, 231-240.

Zinc evidently plays a role in reproduction, appearing with carbonic anhydrase and alkaline phosphatase in the prostate and testes. The amount of zinc found in this tissue, however, is much higher than would normally be associated with the amount of these two enzymes present. Despite the large number of experiments demonstrating the presence and behavior of zinc in the male sex accessory organs, the function of this metal remains obscure. Byar, David P., 1974, Zinc in Male Sex Accessory Organs: Distribution and Hormonal Response, Chapt. 6, Male Accessory Sex Organs--Structure and Function in Mammals.

The toxic effects of zinc ions on human spermatozoa in vitro have also been studied. Lindholmer, C. 1974, Toxicity of Zinc Ions to Human Spermatozoa and the Influence of Albumin, Andologia 6 (1), 7-16. The purpose of this study was to analyze the effects of zinc on the motility and survival of human spermatozoa, and to what extent these effects could be modified by albumin. Collected sperm cells were separated from the seminal fluid by centrifugation and washed in a special solution. The washed cells were divided into two sample groups and 4% human albumin added to one group. A total concentration of 4% albumin was chosen because this corresponds to the total protein concentration of human seminal fluid.

The test results showed that the addition of zinc at a concentration of 5 μg/ml (0.075 mM) to the samples without albumin markedly inhibited sperm motility. By contrast, the addition of zinc at a concentration of 50 μg/ml (0.75 mM) to the samples containing 4% albumin only slightly inhibited sperm motility. The protective effect of the albumin thus was clearly demonstrated.

It is presumed that with the concentration of albumin and zinc normally present in human semen, zinc albumin complexes are formed, some of which may precipitate on the cell surfaces. The biological significance of such precipitate and coating complex is not known, but is assumed to be of importance for protecting the cells against toxic substances in the seminal fluid.

SUMMARY OF THE INVENTION

The present invention is directed to the in vivo chemical control of spermatogenesis and the control of testosterone production in male animals having scrotal testes. This control is provided by the direct injection of a physiologically acceptable astringent into the testes or scrotum.

The effective control of spermatogenesis in the manner taught by this invention is accomplished without the undesirable side effects observed in the methods of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The degree that spermatogenesis and testosterone production are inhibited depends upon the locus of the injection and upon the nature and amount of the astringent. In some cases, it is desirable to inhibit sperm production without affecting the production of testosterone. By a proper selection of astringent and place of injection, it is possible to stop sperm production without significantly affecting the interstitial cells which produce testosterone. It is the production of this male hormone which controls the animal's disposition, sex characteristics and libido.

Suitable astringents are water soluble and are selected from those materials which precipitate proteins. When injected into the testes or scrotum, they must be capable of selectively inhibiting spermatogenesis and the production of testosterone. They must also be physiologically acceptable and produce no undesirable toxic effects.

Such astringents if injected in the scrotum cause tanning of the tunica albuginea. Temperature regulation of the testes is interfered with by this hardening of the tunica which surrounds the testes. Since sex cells are susceptible to injury by a temperature equaling that of the interior body, such treatment provides a method for control of sperm production. In addition to hardening the tunica, some of the astringent penetrates the testes and has the same effect as if injected therein. Such effect, however, is relatively less since most of the astringent does not pass therein.

If injected into the testes, suitable astringents, on the cellular level, cause degeneration of the sex cells in the seminiferous epithelium. This occurs through disintegration of the nuclear and cytoplasmic membranes of the sex cells. It is caused perhaps because the astringents disrupt the chemistry of the testicular fluid between the tubules and cause the tubules to have a hostile environment for the development of sex cells. Depending upon the severity of treatment, the sex cells are progressively affected beginning at the lumen and extending to the periphery of the tubules. Preferably the Sertoli cells and basement membrane of the tubules are left intact, however, under very severe conditions, these are also affected.

If all of the sex cells are destroyed, the treatment is irreversible and results in the complete cessation of sperm production. If some of the sex cells are left, however, it is possible that the epithelium will regenerate and sperm production eventually resume.

In general, a smaller amount of astringent is necessary to stop sperm production if it is injected directly into the testes than if it is injected into the scrotum. Hence by selecting the dose and the locus of the injection, the sex cells can be selectively destroyed thus controlling the exocrine function of the testes in the production of sperm.

By selecting the dose and locus, the endocrine function can also be controlled. For example, it is possible by the present treatment to stop sperm production without affecting the Leydig cells in the stroma between the tubules. If it is desired to reduce the production of testosterone, it is possible to affect the Leydig cells by increasing the dose. This effect may be accomplished with a lesser amount if the astringent is injected directly into the testes.

The male hormone testosterone plays a vital role in the development of the male animal and controls the secondary sex characterisitics, sex impulse and proper maintenance of the genital ducts and accessory glands. The present treatment provides a means for stopping sperm production without otherwise affecting the male, the size of his genitals or his libido. The present treatment optionally provides a means for complete castration if it is desired to stop the production of testosterone as well as the production of sperm. This may be desired, for example, for the purpose of changing the animal's disposition or for the purpose of shrinking his sex organs.

Most of the astringents for use as described above are tannins, zinc salts or combinations thereof. Suitable zinc salts include zinc acetate, zinc chloride and zinc sulfate. When the astringent is tannic acid, it is preferably predissolved in water and the insoluble precipitate of gallic acid separated therefrom by filtration. If a combination of tannic acid and zinc salt is used, it is preferred that an equal stoichiometric amount of each be used. So mixed, as injected, the effective astringent is zinc tannate.

It is preferred that the astringent solution be buffered to a pH from about 4.0 to about 6.5. This is because the pH of the solution affects the absorption and distribution of the drug throughout the scrotum and the testes. While such buffering is also desirable to avoid discomfort to the subject in the form of a stinging sensation, it is not necessary.

Before the astringent is injected, the scrotum should be cleaned with a disinfectant and the needle cleaned before the injection of each testis. This is because the testes are very susceptible to infection.

The selected testis is palpated and the head and tail of the epididymis located. The injection is then given into the midline of the testis. It is important that the injection not be given near the head of the epididymis so that the blood vessels are avoided as they enter the testis. If the injection is given into the blood vessels, the astringent coagulates the blood and forms a clot. It is also important that the injection not be given in the tail of the epididymis. This is because the astringent causes granuloma in fully matured sperm. When one testis has been injected, the other testis is palpated and an injection made into its midline.

The nerves in the testes follow the blood vessels but endings within the tubules seem doubtful. In any case, injection into the scrotum or into the testes does not cause the animal great discomfort.

The volume of the injection, however, does affect the subject's comfort. This is not so critical when the injection is into the scrotum but is highly critical when the injection is into the testes. If too large a volume is injected into the testes, the tubules are ruptured and the subject experiences pain.

The exact amount which can be injected depends, as aforementioned, on the locus of the injection as well as on the species of the animal and size of the particular subject's genitals. The proper amount in each case can be easily determined in view of the examples set forth below.

The following examples and accompanying drawings illustrate the invention. In the drawings,

FIG. 1 is a light micrograph showing a histological section of a control rat testes; and

FIG. 2 is a similar view after treatment with zinc sulfate.

EXAMPLE 1

This example illustrates the effect of zinc sulfate on male reproduction of sexually mature rats when administered orally.

Three hundred sexually mature rats were divided into three groups, Group I being a control. Group II rats were treated daily with 15.0 mg ZnSO₄.7H₂ O and Group III rats with 50.0 mg, both groups receiving said treatment for 30 days.

As shown in Table 1, the data indicate no significant change in the weight of the testes, epididymis, prostate or seminal vesicles. No histological changes were observed in the male reproductive organs and no change in growth rate was observed.

As shown in Table 2, no significant zinc concentration was found in the blood and liver and no change was noted in testosterone levels.

                                      TABLE 1                                      __________________________________________________________________________     ZINC ADMINISTERED ORALLY                                                       Male Rats                                                                             Initial Body                                                                          Final Body                                                                            Testes                                                                               Epididymis                                                                           Prostate                                                                             Seminal Vesicles                        Treatment                                                                             Wt. gm Wt. gm gm    gm    gm    gm                                      __________________________________________________________________________     Control                                                                               224.4 ± 5.75                                                                       411.1 ± 15.02                                                                      3.06 ± 0.10                                                                       0.91 ± 0.03                                                                       0.44 ± 0.01                                                                       0.76 ± 0.05                                        83.3%                                                            15 mg ZnSO.sub.4                                                               orally for 30                                                                  days   211.7 ± 3.77                                                                       365.6 ± 5.06                                                                       2.88 ± 0.17                                                                       0.94 ± 0.03                                                                       0.44 ± 0.03                                                                       0.73 ± 0.04                                        72.7%                                                            50 mg ZnSO.sub.4                                                               orally for 30                                                                  days   223.5 ± 3.59                                                                       408.7 ± 27.13                                                                      2.94 ± 0.13                                                                       0.91 ± 0.04                                                                       0.42 ± 0.02                                                                       0.78 ± 0.04                                        82.9%                                                            __________________________________________________________________________

                                      Table 2                                      __________________________________________________________________________     ZINC ADMINISTERED ORALLY                                                       Male Rats                                                                                     Zn p.p.m. in                                                           Zn p.p.m. in                                                                           24-hr. urine                                                                          Zn μg/ml                                                                           Testosterone                                                                          μM PCA                                  Treatment                                                                             1 gm dry liver                                                                         collection                                                                            in serum                                                                              ng/ml serum                                                                           1 g Liver                                                                             Liver gm                            __________________________________________________________________________     Control                                                                               77.29 ± 1.68                                                                        11.81 ± 0.35                                                                       2.13 ± 0.28                                                                        7.76 ± 0.67                                                                        2.40 ± 0.11                                                                        18.27 ± 0.91                     15 mg ZnSO.sub.4                                                               orally for 30                                                                  days   84.16 ± 1.86                                                                        29.75 ± 10.57                                                                      2.35 ± 0.19                                                                        6.25 ± 1.68                                                                        2.23 ± 0.26                                                                        14.19 ± 0.30                     50 mg ZnSO.sub.4                                                               orally for 30                                                                  days   79.65 ± 1.35                                                                        48.58 ± 7.68                                                                       2.00 ± 0.08                                                                        6.57 ± 0.58                                                                        2.63 ± 0.22                                                                        16.75 ± 0.66                     __________________________________________________________________________      ZnSO.sub.4 solution was made up from ZnSO.sub.4 . 7H.sub.2 O salt.             Therefore 15 and 50 mgZnSO.sub.4 . 7H.sub.2 O correspond to 8.42 mg, 28.0      mgZnSO.sub.4.                                                            

EXAMPLE 2

This example illustrates the effect of zinc sulfate on male reproduction of sexually mature rats when administered intraperitoneally.

Four hundred sexually mature rats were divided into four groups, Group I being a control. The rats in Groups II, III and IV were treated daily for 30 days, respectively, with 0.5, 1.0 and 5.0 mg ZnSO₄.7H₂ O. At the end of 60 days, as in Example 1, the rats were sacrificed.

As shown in Table 3, there was no significant reduction in the weight of the testes, epididymis, prostate or seminal vesicles and no histological changes were observed in the sex organs as compared to the control.

There was, however, a significant reduction in the rate of gain but the testosterone level was not changed. A higher concentration of zinc was found in the liver as shown in Table 4, but the zinc concentration in the testes, epididymis, prostate and seminal vesicles was substantially the same as in the control.

                                      Table 3                                      __________________________________________________________________________     ZINC ADMINISTERED INTRAPERITONEALLY                                            Male Rats                                                                                  Initial Body                                                                          Final Body                                                                            Testes                                                                               Epididymis                                                                           Prostate                                                                             Seminal Vesicles                   Treatment   Wt. gm Wt. gm gm    gm    gm    gm                                 __________________________________________________________________________     Control (H.sub.2 O injected)                                                               208.8 ± 4.6                                                                        406.2 ± 9.07                                                                       2.68 ± 0.15                                                                       0.78 ± 0.07                                                                       0.47 ± 0.02                                                                       0.87 ± 0.19                                        94.5%                                                       0.5 mg ZnSO.sub.4                                                              injected for 30 days                                                                       216.4 ± 1.05                                                                       388.9 ± 6.37                                                                       2.94 ± 0.03                                                                       0.90 ± 0.02                                                                       0.42 ± 0.04                                                                       0.72 ± 0.04                                        *79.7%                                                      1.0 mg ZnSO.sub.4                                                              injected for 30 days                                                                       219.4 ± 3.5                                                                        392.4 ± 10.1                                                                       3.05 ± 0.07                                                                       0.90 ± 0.02                                                                       0.46 ± 0.03                                                                       0.74 ± 0.04                                        *78.9%                                                      5.0 mg ZnSO.sub.4                                                              injected for 30 days                                                                       215.7 ± 2.2                                                                        352.3 ± 12.6                                                                       2.74 ± 0.13                                                                       0.88 ± 0.04                                                                       0.41 ± 0.02                                                                       0.89 ± 0.07                                        *63.3%                                                      __________________________________________________________________________      *Significant reduction of weight gain from the control (p <0.001)        

                                      Table 4                                      __________________________________________________________________________     ZINC ADMINISTERED INTRAPERITONEALLY                                            Male Rats                                                                                       Zn p.p.m.                                                              Zn p.p.m. in                                                                           in 24-hr. urine                                                                         Zn μg/ml                                                                           Testosterone                                                                          μM PCA                                                                             Liver                           Treatment                                                                               1 gm dry liver                                                                         collection                                                                              in serum                                                                              ng/ml serum                                                                           1 g liver                                                                             gm                              __________________________________________________________________________     Control                                                                        (H.sub.2 O injected)                                                                    77.29 ± 1.68                                                                        11.81 ± 1.35                                                                         2.13 ± 0.28                                                                        7.76 ± 0.67                                                                        1.73 ± 0.15                                                                        17.51 ± 0.58                 0.5 mg ZnSO.sub.4                                                              injected for 30                                                                days     92.71 ± 2.37                                                                        22.96 ± 3.40                                                                         2.60 ± 0.10                                                                        6.79 ± 1.34                                                                        1.86 ± 0.24                                                                        14.85 ± 0.48                 1.0 mg ZnSO.sub.4                                                              injected for 30                                                                days     94.27 ± 1.43                                                                        24.29 ± 4.92                                                                         2.48 ± 0.08                                                                        6.87 ± 0.58                                                                        1.62 ± 0.12                                                                        14.99 ± 0.64                 5.0 mg ZnSO.sub.4                                                              injected for 30                                                                days     134.75 ± 15.44                                                                      41.31 ± 8.87                                                                         2.88 ± 0.29                                                                        6.30 ± 0.68                                                                        1.17 ± 0.06                                                                        13.11 ± 0.68                 __________________________________________________________________________      ZnSO.sub.4 solution was made up from ZnSO.sub.4 . 7H.sub.2 O salt.             Therefore 0.5 mg, 1.0 mg and 5.0 mg ZnSO.sub.4 . 7H.sub.2 O correspond to      0.28 mg, 0.56 mg and 2.81 mg ZnSO.sub.4 respectively.                    

EXAMPLE 3

This example illustrates the effect of zinc sulfate on male reproduction in sexually mature rats when administered into the scrotum.

One hundred sexually mature rats were divided into two groups, Group I being a control. Each of the Group II rats was injected with 25 mg ZnSO₄.7H₂ O into each side of the scrotum.

As shown in Table 5, there was a significant reduction in the weight of the testes and epididymis of the treated rats. There was no difference, however, in the weight of the prostate and seminal vesicles.

Histological examination of the testes as shown in FIGS. 1 and 2 showed a significant change in the condition of the sex cells but no difference in the condition of the Leydig cells. This correlated with the finding that there was no significant reduction in testosterone levels as compared with the control.

                                      Table 5:                                     __________________________________________________________________________     ZnSO.sub.4 -7H.sub.2 O INJECTED INTO SCROTUM                                           Body Weight                                                                           Liver Weight                                                                          Testes Epididymis                                                                            Prostate                                                                              Seminal Ves                         Treatment*                                                                             gm     gm     gm     gm     gm     gm                                  __________________________________________________________________________     Control                                                                        0.25 ml H.sub.2 O                                                                      428.0 ± 10.0                                                                       13.26 ± 1.13                                                                       3.57 ± 0.13                                                                        1.23 ± 0.04                                                                        0.80 ± 0.09                                                                        0.98 ± 0.61                      injected into                                                                  each scrotum                                                                   0.25 ml ZnSO.sub.4                                                             7H.sub.2 O = 25 mg                                                                     431.2 ± 17.2                                                                       13.53 ± 0.87                                                                       *1.42 ± 0.09                                                                       *0.56 ± 0.06                                                                       0.82 ± 0.06                                                                        1.20 ± 0.02                      injected into                                                                  each scrotum                                                                   __________________________________________________________________________      *Animals were sacrificed 60 days after                                         *Significantly different from the control (p<0.001)                      

EXAMPLE 4

This example illustrates the effect of zinc sulfate on male reproduction of sexually mature rats when administered in the vas diferens.

Eighty sexually mature male rats were divided into four groups, Group I being a control. The rats in Groups II, III and IV were treated by injecting 0.5, 2.5 and 5.0 mg ZnSO₄.7H₂ O into the vas diferens.

At the end of 60 days, as in the other examples, the rats were sacrificed. There was no significant change in the weight of the testes, prostate or seminal vesicles and no effect on spermatogenesis. There was an increase in the weight of the epididymis, however, in the Group IV rats due to the development of sperm granulomas.

EXAMPLE 5

This example illustrates the effect of zinc sulfate on male reproduction of sexually mature rats when administered in the testes.

Four hundred sexually mature male rats were divided into four groups, Group I being a control. The rats in Groups II, III and IV were treated by injecting 0.5, 2.5 and 5.0 mg ZnSO₄.7H₂ O into the testes. Such injection was made into the midline of each testis with a sterilized needle.

The results of this example showed a significant reduction in the weight of the male reproductive organs, particularly in that of the testes and prostate. The amount of reduction increased with the dose administered and was correlated with a decrease in the testosterone level.

All of the animals from Examples 1-5 were mated with females in heat. Those rats which were treated orally (Example 1) or intraperitoneally (Example 2) with zinc sulfate impregnated the females. Pregnancy also occurred from those animals which had received 0.5 and 2.5 mg ZnSO₄.7H₂ O in the vas deferens while those animals treated with 5.0 mg did not impregnate the females due to sperm granuloma of the epididymis (Example 4). No pregnancy resulted from any of the rats treated in Examples 3 and 5. Only Examples 3 and 5 are in accordance with the present invention. Examples 1, 2 and 4 were conducted for the purpose of comparison.

EXAMPLE 6

This example illustrates a treatment wherein spermatogenesis is stopped without reducing the weight of the testes. This is desired, for example, by some pet owners and usually when the subject is a human male.

Ninety sexually mature male rats were divided into two groups, Group I being a control. The rats in Group II were treated by injecting 0.05 ml into each testis of a drug, herein called Kastrin and containing about an equal amount of zinc sulfate and tannic acid, more particularly containing in this instance 0.25 mg of tannic acid and 0.25 mg of ZnSO₄.7H₂ O.

All of the animals were mated with a female in heat. None of the treated rats impregnated the females. When the rats were sacrificed, it was found that there was no significant difference in the weight of the reproductive organs and that the testosterone levels were not significantly different from the control group.

EXAMPLE 7

As in Example 6, 90 sexually mature rats were divided into two groups, Group I being a control. The rats in Group II were injected with a mixture of zinc sulfate and tannic acid such that 2.5 mg of tannic acid and 2.5 mg of ZnSO₄.7H₂ O was injected into each testis.

The treated rats in Group II were sterile, had smaller testes but there was no change in the testosterone levels as compared to the control group.

EXAMPLE 8

As in Examples 6 and 7, 90 sexually mature rats were divided into two groups, Group I being a control. The rats in Group II were injected with a mixture of zinc sulfate and tannic acid such that 5.0 mg of tannic acid and 5.0 mg of ZnSO₄.7H₂ O was injected into each testis.

The treated rats in Group II were sterile, had smaller reproductive organs and lower testosterone levels as compared to the control animals. More particularly, the testosterone level of Group I was 8.2±0.46 ng/ml as compared to less than 1 ng/ml in the treated animals.

All of the treated animals in Examples 6, 7 and 8 were kept for a year with no mortality. When they were sacrificed, none had abnormal organs, liver, kidney, adrenal, lung or pituitary and no toxic side effect was noted whatsoever.

EXAMPLE 9

As in the previous examples, sexually mature rats were divided into two groups, Group I being a control. The Group II rats were injected with a mixture of zinc sulfate and tannic acid such that 5.0 mg of tannic acid and 5.0 mg of ZnSO₄.7H₂ O was injected into each side of the scrotum into the cavity of the tunica vaginalis.

The treated rats in Group II were sterile and were kept for a year with no mortality. When they were sacrificed, there was no reduction in the weight of the prostate or in the testosterone level as compared to the rats in the control.

When the results of this example are compared with those in Example 8, it is seen that the effect on the endocrine function of the testes is more pronounced when the injection is into the testes as compared to the scrotum.

EXAMPLE 10

The rats in this example were divided and treated as in Example 9 except that the amount of tannic acid and zinc sulfate injected into each side of the scrotum was doubled.

As in Example 9, all of the treated rats were sterile. When the rats were sacrificed, however, there was found a reduction in the weight of all of the reproductive organs and a significant reduction in the testerone levels in the blood.

Thus it is seen that the same effect on the testes can be had by injecting an astringent into the scrotum or into the testes. The amount necessary to achieve a reduction in the endocrine function, however, is more when the drug is injected into the scrotum.

EXAMPLE 11

Six dogs weighing 15 to 22 kg and aging between 8 and 11 years were injected in each testis with 1.0 ml of a mixture containing 100.0 mg of tannic acid and 100.0 mg of ZnSO₄.7H₂ O. Before treatment, two of the dogs were diagnosed with hyperplasia of the prostate, the others with adenocarcinoma. Diagnosis was achieved by rectal and abdominal palpation and by prostate biopsy. All had difficulties in urination.

Each dog was examined weekly. After one month, the prostate was shrunk in size and the animal was able to urinate normally. Thus, surgical castration was made unnecessary and avoided.

This example shows that by controlling the endocrine function of the testes in their production of testosterone a chemical method is provided for the treatment of the prostate. In human males, as in dogs, chronic prostatitis, benign hyperplasia and adenocarcinoma of the prostate are common diseases. The present treatment provides a convenient, relatively risk free, alternative to surgery.

EXAMPLE 12

Two hundred 30-day old male rats, just weaned, were divided into four groups, Group I being a control. The rats in Group I were injected with 0.05 ml of water into each testis. The rats in Group II were similarly injected with 5.0 mg of ZnSO₄.7H₂ O, those in Group III with 5.0 mg of tannic acid and those in Group IV with a mixture (Kastrin) containing 2.5 mg tannic acid and 2.5 mg ZnSO₄.7H₂ O.

The data from this example are reported in Table 6. Forty of the animals were sacrificed 60 days after treatment. The others were watched for a year. The results showed that all of the treated rats were sterile. There was no significant change in the rate of gain.

                                      Table 6                                      __________________________________________________________________________     Effect of Kastrin in Weaned Rats                                                     Initial Final  Liver  Testes                                                                               Epididymis                                                                           Prostate                                                                             Seminal                                Body Wt. (gm)                                                                          Body Weight                                                                           Weight Weight                                                                               Weight                                                                               Weight                                                                               Vesicles Wt.                     Treatment                                                                            *Wt. Gain                                                                              (gm)   (gm)   (gm)  (gm)  (gm)  (gm)                             __________________________________________________________________________     Control                                                                              81.3 ± 4.6                                                                          276.1 ± 18.6                                                                       10.59 ± 0.42                                                                       2.69 ± 0.07                                                                       0.80 ± 0.02                                                                       0.23 ± 0.02                                                                       0.25 ± 0.02                         242%*                                                                    Group II                                                                             81.3 ± 5.4                                                                          267.3 ± 14.7                                                                       9.95 ± 0.54                                                                        0.21 ± 0.04                                                                       0.10 ±  0.03                                                                      0.05 ± 0.02                                                                       0.05 ± 0.02                         229%*                                                                    Group III                                                                            86.7 ± 3.8                                                                          270.9 ± 15.4                                                                       10.40 ± 0.43                                                                       0.46 ± 0.12                                                                       0.31 ± 0.07                                                                       0.10 ± 0.05                                                                       0.14 ± 0.04                         212%*                                                                    Group IV                                                                             82.3 ± 3.2                                                                          267.7 ± 11.2                                                                       11.32 ± 0.33                                                                       0.21 ± 0.02                                                                       0.19 ± 0.02                                                                       0.06 ± 0.02                                                                       0.06 ± 0.02                         225%*                                                                    __________________________________________________________________________      *Rate of Gain                                                            

EXAMPLE 13

Thirty-eight litter mate dogs, 8 weeks old, were divided into four groups. The dogs in Group I were a control and were injected with 0.2 ml of water into each testis. The animals in Group II were similarly treated in each testis with 20.0 mg of tannic acid buffered to a pH of 6.5. Those in Group III were treated with 20 mg of ZnSO₄.7H₂ O and those in Group IV with a mixture of 10 mg of tannic acid and 10 mg of ZnSO₄.7H₂ O.

None of the treated animals impregnated females when they reached the age of sexual maturity. There were no significant differences, however, in the rate of growth, development of the urinary tract or development of the pelvic bones as documented by X-ray. In fact, the dogs in Group II which were treated with tannic acid showed better muscular appearance than those in the control group.

Two years after treatment, all of the dogs in Groups II, III and IV were healthy, active and showed no adverse side effects whatsoever. The only difference between them and those in the control was that the treated dogs were sterile and had smaller testes. There was, however, no difference in libido.

EXAMPLE 14

Fifty sexually mature dogs were divided into two groups. Twenty, each weighing less than 15 kg, were injected in each testis with 0.5 ml of an aqueous mixture containing 2.5 mg of tannic acid and 2.5 mg of ZnSO₄.7H₂ O. The remaining dogs, each weighing between 20 and 35 kg, were injected in each testis with 1.0 ml of a mixture containing 5.0 mg of tannic acid and 5.0 mg of ZnSO₄.7H₂ O.

Before treatment, the semen of each dog was evaluated. On average, the volume was 5.5 ml, the motility 4+, the sperm count 400×10⁶ /ml, the pH 6.2 and the morphology 4% with coiled tails and 2% tailless with 8 to 10% dead.

Forty eight hours after treatment, the semen of each dog was again evaluated. On average, the volume was 5.5 to 6.0 ml, the motility 1+, the sperm count 400×10⁶ /ml, the pH 6.3 and the morphology 70% with coiled tails and 20% tailless with 100% dead. After one week, the volume was 4.0 ml, the motility 0, the sperm count 10×10⁶ /ml, the pH 6.2 and the morphology 96% with coiled tails and 4% tailless with 100% dead.

The semen of each dog was evaluated again after two weeks, one month, three months, six months, one year and two years. In each case, no live sperm were found.

Needle testicular biopsies were taken before treatment, ten months after and two years after. Histological examination showed the absence of spermatogenesis after treatment as compared to the normal condition existing before.

EXAMPLE 15

Sexually mature dogs were treated in this example as in Example 14 except that they were injected in each testis with 0.1 ml of a solution containing 5.0 mg of tannic acid and 5.0 mg of ZnSO₄.7H₂ O.

One week after treatment, the sperm count dropped from 400×10⁶ to 1-5×10⁶ /ml. Six months after treatment, the sperm count had recovered somewhat to 10×10⁶ /ml. At the end of two years, the sperm count was substantially normal. Other dogs which had been repeatedly injected with the same amount of the drug were made permanently sterile.

This example illustrates that by controlling the dose, the exocrine function of the testes can be inhibited temporarily. It also illustrates that a dose insufficient to cause permanent sterility if administered only once can induce permanent sterility if administered several times.

EXAMPLE 16

Thirty sexually mature cats weighing 4.3±0.2 kg were divided into three groups, Group I being a control. Those animals in Group I were injected in each testis with 0.1 ml of water. Those in Group II were injected with 10.0 mg of tannic acid buffered to a pH of 6.8 and those in Group III with 5.0 mg of tannic acid and 5.0 mg of ZnSO₄.7H₂ O.

Before treatment and after in the case of the control group, the average sperm count was 230×10⁶ /ml. One week after treatment, the sperm count for the animals in Groups II and III was zero.

All of the animals were observed for one year and bred with female cats in the spring and fall. None of the treated animals impregnated the females. The testosterone level for the cats in Group I was 6.8±0.2 ng/ml, for those in Group II 4.1±0.3 ng/ml and less than 1 ng/ml for those in Group III.

The cats in Groups I and II acted normally but those in Group III exhibited no normal male aggressiveness. The urine of Group III also lacked characteristic odor. None of the animals in Groups II or III gained any more weight than those in Group I. In other words, the treated animals did not become obese like surgically castrated animals.

EXAMPLE 17

Ten purebred Angus bulls weighing an average of 400 pounds were divided into five groups, Group I being a control. Each animal in Group I was injected with 5.0 ml of water in each testis. Those in Group II were surgically castrated. The animals in Group III were injected with 500.0 mg of tannic acid, those in Group IV with 500.0 mg of ZnSO₄.7H₂ O and those in Group V with 250.0 mg of tannic acid and 250.0 mg of ZnSO₄.7H₂ O.

The animals were fed concentrate and grazed. After one year, they were sacrificed. All of the animals passed federal inspection for consumption by humans.

As shown in Table 7, all of the animals in Groups III, IV and V had a faster rate of gain than the surgically castrated animals in Group II. The animals in Group V had better carcass quality than that of any other group. No significant concentrations of zinc or tannic acid were found in the muscle, blood, spleen, heart, liver or kidney of the treated animals as compared to Groups I and II.

The data therefore indicate that the present treatment provides a safe means for castrating cattle, which in some instances provides better rate of gain and carcass quality as compared with surgical castration.

                  Table 7                                                          ______________________________________                                                   BODY WEIGHT            %      %                                      TREATMENT Initial Final   Rate of Gain                                                                            Protein                                                                               Fat                                  ______________________________________                                         Group I   384     960     1.79 lbs/day                                                                            17.0   24.0                                 Group II  498     912     1.29 lbs/day                                                                            18.1   19.5                                 Group III 376     826     1.40 lbs/day                                                                            18.3   18.0                                 Group IV  414     910     1.54 lbs/day                                                                            17.9   20.9                                 Group V   406     1062    2.04 lbs/day                                                                            17.7   22.5                                 ______________________________________                                    

In addition to the above, the present treatment can be used on male sheep, pigs, horses and other similar mammals having scrotal testes, including human males.

Recommended dosages, as above mentioned, depend upon the size and species of the animal and upon the desired result. Recommended dosages for sterilization of adult dogs weighing less than 10 kg is 0.25 ml into each testis of a mixture containing between 10.0 and 25.0 mg of tannic acid and 25.0 mg of ZnSO₄.7H₂ O. For dogs weighing between 10 and 15 kg, the recommended dose is 0.5 ml into each testis of a mixture containing between 10.0 and 50.0 mg of tannic acid and 50.0 mg of ZnSO₄.7H₂ O. For those dogs weighing between 16 and 20 kg, the recommended dose is 1.0 ml into each testis of a mixture containing between 50.0 and 100.0 mg of tannic acid and between 75.0 and 100.0 mg of ZnSO₄.7H₂ O. For dogs weighing over 20 kg, the recommended dose is 1.0 ml in each testis of a mixture containing between 50.0 and 125.0 mg of tannic acid and 125.0 mg of ZnSO₄.7H₂ O.

In the case of puppies between 6 and 8 weeks of age, the recommended dose is 0.05 ml into each testis of a mixture containing 2.0 mg of tannic acid and 5.0 mg of ZnSO₄.7H₂ O. For puppies over 8 weeks but not sexually mature, the dose is preferably 0.08 ml into each of the testes of a mixture containing 7.0 mg of tannic acid and 7.0 mg of ZnSO₄.7H₂ O. For adult cats, the recommended dose is 0.1 ml into each testis of a mixture containing 10.0 mg of tannic acid and 10.0 mg of ZnSO₄.7H₂ O.

When tannic acid and zinc sulfate are administered in each testis in the above-mentioned recommended amounts, the treatment has been found effective to arrest spermatogenesis. Since zinc is normally present in seminal fluid, such treatment adds a minimum of foreign material to the body of the animal. Moreover, the drug remains substantially localized in the immediate area of the injection. When the astringent is zinc sulfate, for example, there is some diffusion of the zinc to the epididymis and prostate, but no diffusion beyond that. When the astringent is a combination of a zinc compound and a tannin, there is even less tendency for the zinc to diffuse. Such combinations are, for that reason, preferred.

Most of the experimental work reported in the above examples was performed by injection of the drugs with a needle. It is to be understood that other means of subcutaneous penetration may also be employed as desired.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. More particularly, a chemical compound and treatment is taught whereby the exocrine and endocrine function of the testes are controlled.

As various changes could be made in the above described compounds and treatment without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 

What is claimed is:
 1. A method for selectively inhibiting spermatogenesis and the production of testosterone comprising injecting an effective amount of a chemical sterilant selected from the group consisting of a water soluble physiologically acceptable zinc compound, tannin and mixtures thereof, capable of selectively inhibiting spermatogenesis and the production of testosterone into the testes or scrotum of a male animal having scrotal testes.
 2. The method according to claim 1 wherein the injectable chemical sterilant includes zinc compound and tannin, said tannin capable of combining with the zinc compound to inhibit the transport of zinc from the testes or scrotum of the subject male animal.
 3. The method according to claim 2 wherein the volume of the chemical sterilant injected into the testes or scrotum of the subject male animal is such that it does not rupture said scrotum or testes.
 4. The method according to claim 3 wherein the zinc compound and the tannin are present in stoichiometrically equal amounts in said volume sufficient effectively to suppress the production of sperm substantially but insufficient effectively to suppress the production of testosterone substantially.
 5. The method according to claim 3 wherein the zinc compound and the tannin are present in stoichiometrically equal amounts in said volume sufficient effectively to suppress the production of sperm substantially and effectively to suppress the production of testosterone substantially.
 6. The method according to claim 4 wherein the animal is a dog.
 7. The method according to claim 4 wherein the animal is a cat.
 8. The method according to claim 4 wherein the animal is a cow.
 9. The method according to claim 4 wherein the animal is a human being.
 10. The method according to claim 5 wherein the animal is a dog.
 11. The method according to claim 5 wherein the animal is a cat.
 12. The method according to claim 5 wherein the animal is a cow.
 13. The method according to claim 5 wherein the animal is a human being.
 14. A method for selectively inhibiting spermatogenesis and the production of testosterone comprising the sequential steps of selecting a male animal having scrotal testes, disinfecting the skin of the scrotum and injecting an effective amount of a mixture of a water soluble physiologically acceptable zinc compound capable of selectively inhibiting spermatogenesis and the production of testosterone and a water soluble physiologically acceptable tannin capable of combining with the zinc compound to inhibit the transport of zinc from the testes or scrotum of the subject male animal in water solution buffered to a pH from about 4.0 to about 6.5 into each tunica vaginalis.
 15. The method according to claim 14 wherein the amount of zinc compound and tannin in the mixture injected into each tunica vaginalis is sufficient effectively to suppress the production of sperm substantially but insufficient effectively to suppress the production of testosterone substantially.
 16. The method according to claim 14 wherein the amount of zinc compound and tannin in the mixture injected into each tunica vaginalis is sufficient effectively to suppress production of sperm and sufficient effectively to suppress the production of testosterone substantially.
 17. A method for selectively inhibiting spermatogenesis and the production of testosterone comprising the sequential steps of selecting a male animal with scrotal testes, disinfecting the skin of the scrotum, palpating the scrotum to locate the epididymis of a first testis, injecting an effective amount of a chemical sterilant consisting of a water soluble physiologically acceptable zinc compound capable of selectively inhibiting spermatogenesis and the production of testosterone and a water soluble physiologically acceptable tannin capable of combining with the zinc compound to inhibit the transport of zinc from the testes or scrotum of the subject male animal in water solution buffered to a pH from about 4.0 to about 6.5 into the midline of the first testis in such a way that the head and tail of the epididymis of the first testis is avoided, palpating the scrotum to locate the epididymis of a second testis and injecting an effective amount of said chemical sterilant into the midline of the second testis in such a way that the head and tail of the epididymis of the second testis is avoided.
 18. The method according to claim 17 wherein the amount of chemical sterilant injected into each testis is sufficient to suppress the production of sperm substantially but insufficient to suppress the production of testosterone substantially.
 19. The method according to claim 17 wherein the amount of chemical sterilant injected into each testis is sufficient to suppress the production of sperm and the production of testosterone substantially. 